Electron multiplier tube with a tapered collector and internal interelectrode decoupler



Sept. 2, 1969 M. BETOULE ET AL 3,465,190

ELECTRON MULTIILIER TUBE WITH A TAPERED COLLECTOR AND INTERNAL INTERELECTRODE DECOUPLER Filed Jan. 15, 1968 3 Sheets-Sheet 1 MICHEL BETWL E 'FPEW BY i /fi AGENT Sept. 2, 1969 M. BETOULE ET AL 3,465,190

ELECTRON MULTIPLIER TUBE WITH A TAPERED COLLECTOR AND INTERNAL INTERELECTRODE DECOUPLER Filed Jan. 15, 1968 3 Sheets-Sheet 5 INVENTO MICHEL arrows RS PIERRE 'nsnmrs BY Rene P n United States Patent Int. Cl. I-i01 43/06 US. Cl. 313--105 5 Claims ABSTRACT OF THE DISCLOSURE An electron multiplier which includes a dynode for the emission of secondary electrons and an anode for collecting the secondary electrons both of which form bodies of revolution about a common axis, the electrode nearest the axis of revolution having an electrically conductive extension which also forms a body of revolution about the aforesaid axis and which tapers and connects to an inner conductor of a coaxial conductor of an output lead while the outer conductor of the coaxial conductor is connected to a screen for limiting waves produced between the electrodes which also forms a body of revolution about the axis.

The invention relates to an electron multiplier tube comprising a dynode for the emission of secondary electrons and an anode for collecting the secondary electrons emitted by the dynode, these two electrodes forming bodies of revolution about a common axis.

In known electron multiplier tube of this kind the output signals are derived from the tube through a common, single, electrically conductive wire.

There is known an electron multiplier tube in which a coaxial signal output conductor is provided in the bottom of the tube. Herein the collector is formed by a flat, circular collector-electrode surrounded by an auxiliary electrode which provides a course of the field lines conductive to the collection. Moreover, this auxiliary electrode forms an electrostatic screen around the collectorelectrode. The connection between the collector and the inner conductor of the coaxial output conductor is for-med by a common electrically conductive wire. The connection between the auxiliary electrode and the outer conductor of the coaxial lead is established in the same manner. In practice a decoupling capacitor is provided outside the electron multiplier between the two last dynodes of the tube. This output arrangement has the disadvantage that adaptation cannot be carried out easily.

There is furthermore known an electron multiplier tube in which the collector comprises a special electron lens formed by a cylinder and plates being at a suitable potential for focusing the secondary electrons'from the last dynode at a focus lying on a disc-shaped collector-electrode, which is directly connected to the end of the inner conductor of a coaxial output lead. The signal energy propagates in a direction to the outside along the coaxial output lead, which terminates at the place of the collectorelectrode by the interruption of the inner conductor. In the opposite direction the wave strikes the cylindrical conductor, the diameter of which may be chosen as a function of the desired cutoff frequency.

The invention has for its object to provide a rapidly responding electron multiplier tube having a coaxial structure of revolution of the electrodes, which permits a ready adaptation of the output impedance and which exhibits less disturbance of the output signals than the known 3,465,190 Patented Sept. 2, 1969 ice electron multiplier tubes having a coaxial structure of revolution.

In an electron multiplier tube comprising a dynode for the emission of secondary electrons and an anode for collecting these secondary electrons, these two electrodes forming bodies of revolution about a common axis, the one electrode, which is nearest the axis of revolution has, in accordance with the invention, an electrically conductive prolongation which forms a body of revolution about said axis and which concentrates to the inner conductor of a coaxial output lead, whose outer conductor is connected to a screen for limiting the waves produced between said electrodes, said screen forming a body of revolution about said axis.

In this electron multiplier tube the last dynode or the anode forms part of a coaxial output lead. The characteristic impedance thereof may be suitably chosen by the choice of the correct shape of the coaxial output lead.

Said prolongation and said screen preferably form two conical surfaces, the apices of which are orientated to the same side. The characteristic impedance of the coaxial line, then having the form of a frustrum may be adapted to the desired value by a correct choice of the apices of the conical surfaces in accordance with known rules.

The space between the dynode and the anode preferably opens out in the space between said prolongation and said screen in order to minimize disturbance of the waves.

In particular embodiments the electron multiplier tube comprises an anode which is at least partly cylindrical.

In the embodiment described above for the output stage of the electron multiplier tube the integration of decoupling members inside the tube can be readily carried out. The invention therefore relates particularly to an electron multiplier tube in which at least one inter-electrode decoupling member is incorporated inside the tube.

The invention will be described more fully with reference to the accompanying drawing, in which-- FIG. 1 is a sectional view of the upper part and the lower part of one embodiment of an electron multiplier tube according to the invention,

FIG. 2 shows part of the input stage of the tube of FIG. 1,

FIG. 3 shows an amplifying stage of the tube of FIG. 1.

The input stage comprises a photocathode 1 provided on the rear side of a front plate 2 of glass. The front plate is sealed to a metal ring 3, to which the further part of the tube envelope 4 is secured and which serves as an electric connection for the photocathode 1. A first focusing electrode F is formed by a wire 5, secured to the centre of the photocathode 1, land a tube 6. A second electrode F is formed by applying aluminium from the vapour phase to the tube envelope. The focusing electrode F is at the potential of the photocathode 1 and the focusing electrode F is connected to a voltage source (not shown) via a through-connection 7. A first acceleration electrode A and a second acceleration electrode A are at the potential of the first dynode S The shape of the photocathode 1, which forms a body of revolution about the tube axis, is accurately indicated in the drawing. The shape of the photocathode and the position of the focusing electrodes permit of obtaining, by means of a circlesection beam of radiation, a beam of photoelectrons of annular section, which is collected substantially completely on the first dynode S The active surface of the photocathode is an annular surface between circles of diameters of mms. and 3 mms. respectively. Theoretically 99.9% of the photoelectrons is collected in this case. FIG. 2 represents the configuration of the electric field in the input stage of the tube of FIG. 1 in the form of a plurality of equipotential lines, one of which is designated by 8 and one by 9. In FIG. 2 accurate trajectories of the elec- 3 trons are shown. One of these trajectories is indicated by 10.

The amplifying stages of the tube of FIG. 1 are subject matter of the co-pending application Ser. No. 697,801, filed Jan. 15, 1968, of the applicant. The amplifying stages comprise, as is Shown in FIG. 1, outer dynodes designated by odd ordinal numerals S S and ff. and inner dynodes designated by even ordinal numerals S S and ff. The dynodes S S S S etc. are supported from electrically conductive discs D D D D etc. The discs are sealed to rings R lying between them and serve as electric conductors for the dynodes. The conductors are connected in known manner to positively progressing voltages adapted to ensure satisfactory characteristics of linearity and fastness of response. FIG. 3 is an elevation of an amplifying stage of the tube from FIG. 1. The amplifying stage is shown in FIG. 3 partly broken away. This amplifying stage comprises the outer dynodes S and the inner dynode S The outer dynode S is secured to an annular support 11 having a connecting tab 12 for connection with the dynode S and a tab 13 for connecting with the disc D The shape of the support 11 ensures an excellent mechanical rigidity. The inner dynode S is supported from tWo crossed wires 14 and 15 of metal, secured to a support 16, which bears on the disc D The dynode 8;; has passages 17 for the metal wires 14 and 15. Also the connection of the inner dynode ensures a satisfactory mechanical rigidity, while the connecting means practically can not affect the flow of electrons.

The part of the tube of FIG. 1 which is essential for the ideaof the invention is formed by the output stage. The output stage comprises (see FIG. 1) a cylindrical anode 18, having a conical prolongation 19, which is connected mechanically and electrically to the inner conductor 20 of a coaxial output lead C, sealed in the bottom of the tube. The outer conductor 21 of the coaxial output lead C is connected to a conductive truncated cone 22, which surrounds the anode coaxially. At 23 and 24 the tube includes as integrated capacitance for the decoupling of the electrodes. The members 19 and 22 form a coaxial lead having a characteristic impedance of 50 ohms so that the output of the electron multiplier can be readily connected to signal detection apparatus. A space 100,

between anode 18 and last dynode Sn opens out into space 101 between prolongation 19 and screen 22 in order to minimize disturbances of the output waves.

What is claimed is:

1. An electron multiplier tube comprising a dynode for the emission of secondary electrons and an anode for collecting said secondary electrons, these two electrodes forming bodies of revolution around a common axis, one of said electrodes being located nearest the axis of revolution having an electrically conductive prolongation forming a body of revolution about said axis and concentrating to an inner conductor of a coaxial output lead, the outer conductor of which is connected to a screen for limiting the waves produced between said electrodes, said screen forming a body of revolution around said axis.

2. An electron multiplier tube as claimed in claim 1 in which said prolongation and said screen form conical surfaces, the apices of which are orientated to the same side.

3. An electron multplier tube as claimed in claim 1 in which the space between said dynode and said anode opens out into a space between said prolongation and said screen.

4. An electron multplier tube as claimed in claim 1 in which the anode is at least in part cylindrical.

5. An electron multplier as claimed in claim 1 in which at least one interelectrode decoupling member is incorporated inside the tube.

References Cited UNITED STATES PATENTS 2,424,850 7/1947 Roman 3l3105 X 2,433,724 12/1947 Wolfgang 3l3105 X 2,695,984 11/1954 Giacoletto 313-103 X 3,176,178 3/1965 Goodrich et al 313-104 3,183,390 5/1965 Grader et al 313105 X JAMES W. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner US. Cl. X.R. 

